Method accurately measures the thermal conductivity of high-performance sheet insulation as a discrete function of temperature. It permits measurements to be made at temperature drops of approximately 10 degrees F across the insulation and ensures measurement accuracy by minimizing longitudinal heat losses in the system

Hyde, E. H.

Russell, L. D.

English

NASA Technical Reports Server

Longitudinal Heater 
End Heater
Thermo-couples
January 1968	 Brief 68-10013 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Method of Measuring Thermal Conductivity of High Performance Insulation 
-' 
Test Heater	 End Heat-- 
Insulation 
A method has been developed for accurately meas-
uring the thermal conductivity of high-performance 
sheet insulation as a more discrete function of tem-
perature than could be measured by previous 
methods. The new method permits measurements to 
be made at temperature drops of only approximately 
10°F (compared to at least 200° F previously required) 
across the insulation and ensures measurement 
accuracy by minimizing longitudinal heat losses in 
the system. 
This method of measurement employs a silicone 
resin—fiberglass tube approximately 3 feet long, with a 
3-inch outside diameter and a 1/16-inch wall, as the 
support for the insulation. Heater wires of 6-mil 
copper are wound around the entire length of the sup-
port tube. The windings constitute 5 heaters. The 
"test heater," one foot long, is at the center portion 
of the tube. Two "longitudinal heaters" bracket the 
test heater to simulate the infinite cylinder effect. Two 
"end heaters," each I inch long, complete the unit. 
Separate variable power controls, one for each of the 
5 heaters, ensure a uniform temperature over the
entire length of the unit. Test specimens of the insula-
tion are wrapped around the heater wires. Thermo-
couples are positioned to monitor temperatures at 
both the inner and outer surfaces of the insulation 
specimens. 
To make a series of measurements, the conductivity 
apparatus with the insulation wrapping is mounted in 
a jacketed vacuum chamber. The chamber is evacu-
ated and the fluid flow is started in the jacket on a 
heating or cooling cycle to attain the desired ambient 
temperature in the chamber. When this temperature is 
reached, electric power is turned on to the heaters 
under the insulation specimen until the 10°F differ-
ential temperature inside-to-outside the insulation is 
reached. The temperature gradients within the speci-
men are held to a minimum by manipulating the 
individual heater controls as the differential tempera-
ture is approached. The voltages across the individual 
heaters are monitored as the test proceeds. A data 
point is considered to have been attained when the 
longitudinal temperature gradients are less than 
0.050 F/ft for a period of at least three hours. The time 
(continued overleni( 
MW
This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19680000013 2020-03-12T05:42:29+00:00Z
required to attain a significant data point averages 
from 18 to 24 hours. At this time (at thermal equilib-
rium), the thermocouple readings are converted to 
yield the outer and inner surface temperatures of the 
insulation (and the values of the longitudinal tempera-
ture gradients). The value of the heat flux is calculated 
from the measured current and voltage in • the test 
heater. Since the internal and external radii and 
length of the insulation are known, the thermal con-
ductivity is readily calculated by substituting the 
values of the experimental data into the standard log 
mean temperature formula. Slight temperature varia-
tions from the thermal equilibrium point and longi-
tudinal gradients can be taken into account analyti-
cally.
Note: 
Details concrning this method of measurement 
may be obtained from: 
Technology Utilization Officer 
Marshall Space Flight Center 
Huntsville, Alabama 35812 
Reference: B68-10013 
Patent status: 
No patent action is contemplated by NASA. 
Source: E. H. Hyde 
of Marshall Space Flight Center 
and L. D. Russell 
of Lockheed Missiles and Space Company 
under contract to 
Marshall Space Flight Center 
(M FS- 14088) 
Brief 68-10013	 Category 02


Method of measuring thermal conductivity of high performance insulation

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server